We have decided as a society that the rich should pay more taxes. We have a progressive tax system, where the more one makes the higher percentage of their income goes to Uncle Sam... and thereby increasing the amount twice (once because it is a percentage of a larger sum, and once because the percentage itself is higher). The rich pay plenty. Could they "afford" more? Probably. Should they pay more?
In reality, the rich have many tax breaks, like being able to inherit assets without paying for the assets' appreciation.
And even with these breaks, 85% of the taxes are paid by the top 25% of the population. As the kids say, "is that fair?" And as you see in the graph above, the "rich" are paying a higher percentage of their income as well. Some say they are being taxed to death.